1. Field of the Invention
This invention relates in general to wear bushings and, in particular, to a wear bushing that measures the elevation of lock ring grooves on an inner diameter of a wellhead housing prior to running a lockdown hanger or locking ring bridging hanger.
2. Brief Description of Related Art
Following setting of a casing hanger, a wear bushing is often landed axially above the casing hanger. This is done prior to further drilling operations that may be conducted axially downhole from the casing hanger. The wear bushing protects the casing hanger and wellhead housing from damage and wear that might be caused by the drill bit and drill string during these operations downhole from the casing hanger. Generally, the casing hanger is set, then a casing hanger running tool that was used to land and set the casing hanger is pulled from the wellbore. A wear bushing running and retrieval tool is coupled to the drill string in place of the casing hanger running tool. The wear bushing running and retrieval tool runs, lands, and sets the wear bushing. After landing the wear bushing, the wear bushing running and retrieval tool may pressure test the wear bushing to ensure that the wear bushing has properly landed on the casing hanger.
Following a successful pressure test, the wear bushing running and retrieval tool is decoupled from the wear bushing and pulled from the wellbore. Various drilling tools may then be attached to the drill string in place of the wear bushing running and retrieval tool. The drilling tools are then run downhole past the wear bushing and the casing hanger to conduct drilling operations. Preferably, the drill tool and drill string will pass through a bore of the casing hanger without contacting or damaging the inner diameter or the rim of the casing hanger. However, if the drill tool is misaligned relative to the casing hanger, the drill tool may contact and damage the casing hanger as it passes through the casing hanger. If a wear bushing is landed axially above the casing hanger, the drill tool will first contact the wear bushing, and, as the drill tool passes through the wear bushing, it will come into alignment with the casing hanger. Thus, the wear bushing protects the casing hanger. In addition, if the drill string rotates eccentrically during the drilling operation, the drill string will contact and wear the wear bushing rather than the casing hanger, thus protecting the casing hanger. After performance of the desired drilling operations, the drill string and the drill tool will be pulled from the wellbore. The wear bushing running and retrieval tool may then be coupled to the drill string in place of the drill tool, and then be run to the wear bushing to pull the wear bushing from the wellbore.
Typically, a lockdown hanger may then be run downhole to land and set above the casing hanger to provide additional casing lockdown capability. The lockdown hanger may be needed due to thermal expansion of the casing string. Lockdown hangers improve long-term seat reliability below the lockdown hanger by sharing the cyclic axial loads applied to the casing hanger. To properly land and set a lockdown hanger, the lockdown hanger must be run proximate to lock-ring grooves formed in the subsea wellhead axially above the casing hanger. After landing, a grooved ring of the lockdown hanger will actuate to engage the lock-ring grooves, thereby properly securing the lockdown hanger to the wellhead and casing hanger. Operation of the rig would generally require running of a lead impression tool prior to running and setting of the lockdown hanger. The lead impression tool determines the elevation of the lock-ring grooves for proper landing of the lockdown hanger. However, this step is often bypassed due to the costs associated with performing an additional tool trip with the drilling rig. Typically, the lockdown hanger is run, landed, and set without checking the locking ring groove elevation. If there is a problem with the lockdown hanger, the lockdown hanger may then be removed and the elevation of the locking ring grooves checked with the lead impression tool. This adds an additional downhole trip and can significantly increase the costs associated with completion of a well. Therefore, a lead impression tool that determined lock-ring groove elevation without requiring an additional rig trip would be useful in ensuring more efficient rig operation and fewer problems in completion of the well.